1. Field of the Invention
The present invention relates to a plane magnetic recording medium.
2. Description of the Prior Art
The plane magnetic recording mediums have been widely used as a memory element for the data processing apparatus and it has a magnetic layer coated on a disc substrate made of polyester, etc. The magnetic recording mediums commercially available have been treated by processes for writing-in track numbers, sector numbers and other necessary data which is referred to as "initiallizing".
FIG. 1 shows one embodiment of the initiallized magnetic recording medium wherein the reference numeral (1) designates a magnetic recording medium formed in disc shape; (1a) designates a central opening formed at the axial center of the magnetic recording medium (1) and (2) designates a data track initiallized in coaxial relation with the central openin (1a). Each data track is equally divided into a number of sections such as 26 sections in the radial direction to form the corresponding number of sectors (3). Each sector (3) consists of an ID field (3a) and a data field (3b) as shown in FIG. 2.
An operator reads the ID field (3a) from the initiallized data track (2) to confirm the track numbers or the sector numbers and then data can be written in the data field (3b) or the written data is read out from the data field.
Thus, in the conventional magnetic medium, the initiallizing has been given so that the width of the data track is identical (2) with an effective width (such as 300.+-.25 .mu.m) of the magnetic head for the write-in and read-out of the flexible disc apparatus. However, even though the data track (2) is initiallized to be in a precisely coaxial circle about the physical center 0 of the magnetic recording medium (1), a revolutional center 0' of the magnetic recording medium as chucked is deviated from the physical center 0 of the same (FIG. 3) because of the tolerance of the central opening (1a) and the tolerance of the flexible device for chucking the magnetic recording medium whereby a trace (4) of the magnetic head is deflected from the data track (2). Thus, a reproducing output induced in the magnetic head is varied depending upon the revolution of the magnetic recording medium (1).
The variation of the reproducing output is referred to as modulation. When the modulation is caused, a missing error is easily caused in low reproducing output range (a) and an extra error is easily caused in high reproducing output range (b), disadvantageously.
The threshold level is also varied by the level variation of the reproducing output to cause unstable operation.